Implementing an algorithm to determine if a string has all unique characters [closed]

Answer 1

Solution 1:

def is_unique(string):
  if len(string) > 128:
    return False

  unique_tracker = [False] * 128
  for char in string:
    if unique_tracker[ord(char)] == False:
      unique_tracker[ord(char)] = True
    else:
      return False
  return True

Solution 2:

def is_unique_bit(string):
  if len(string) > 128:
  return False

  unique_tracker = 0
  for char in string:
    ascii_val = ord(char)
    if (unique_tracker & (1 << ascii_val)) > 0:
      return False
    unique_tracker |= (1 << ascii_val)
  return True

Answer 2

The solution you have translated from Java into Python is what's called a 'bit-twiddling' algorithm. The idea is that an integer can be treated in multiple ways: One, as a number. Two, as a collection of bits (32 off/ons, or 64, or what-have-you). The algorithm bit-twiddles by saying each bit represents the presence or absense of a specific character - if the nth bit is 0, it sets it. If it's 1, the character that bit corresponds to already exists, so we know there are no unique characters.

However, unless you need the efficiency, avoid bit-twiddling algorithms, as they're not as self-evident in how they work as non-bit-twiddles.